A packet switching communication system comprises a plurality of communicating devices, such as computers, terminals, telephones, or data sets (referred to as hosts), that are interconnected for communication through a plurality of switching networks. Interconnection of the hosts to the switching networks, and of the switching networks to each other, is commonly accomplished by means of communication trunks. The trunks are coupled at each end either to a host by a host interface or to a switching network by a trunk controller. The switching networks generally comprise a plurality of switching nodes that function to connect communications incoming on a trunk to the appropriate one of a number of outgoing trunks, depending upon the destination of the communication. Such packet switching systems are well-known in the art. A representative packet switching system is disclosed in U.S. Pat. No. 4,491,945, to J. S. Turner, entitled "Fast Packet Switch", filed on June 25, 1982, and assigned to the same assignee as this application.
Each switching node is the basic switching element of a packet switching network. The design and characteristics of nodes vary widely from system to system. However, a common type of node has two serial signal inputs and two serial signal outputs. A packet of serial signals arriving at a node input is generally buffered within the node. Based on address information carried by the packet, the packet signal stream is then directed to either one of the two node outputs.
In multi-node packet networks, the outputs of some nodes are connected in regular patterns to inputs of other nodes to form a node matrix, or array. This array of interconnected nodes constitutes the switching fabric, or switching body, of a switching network.
The switching nodes that constitute a switching network are generally distributed over a plurality of circuit packages. To connect the outputs of nodes of one circuit package to the inputs of nodes of another circuit package, the packages are interconnected for communication by communication links. For example, the electronic components of the nodes are mounted on a plurality of circuit boards, or cards. The circuit cards are then plugged into a backplane, whose conductors serve to interconnect the cards.
As miniaturization of circuit components progresses, through techniques such as large-scale or very large-scale integration of semiconductor circuits, more and more nodes may be fitted into a single circuit package. Circuit miniaturization has many benefits such as reduced device size, lower device power dissipation, improved performance due to reduced signal propagation delays, and lower cost. But as a consequence of greater circuit densities, increasingly larger numbers of input and output signal contact positions, such as contact pins, are required on each circuit package to provide for the requisite interconnection thereof with other circuit packages. In the current technology, the contacts take up significant amounts of space in a circuit package relative to the space occupied by the circuitry. A circuit package is therefore often limited in the number of nodes that it can contain by the maximum number of contacts that can be made to the package. Hence, conservation of contacts is important, and keeping the number of necessary contacts to a minimum is a principal circuit design objective.
A further limitation imposed on packet switching system design by current technology is the speed of operation of the switching nodes. The operational speed of the nodes is constrained by technology of the logic that is used to implement the nodes, such as transistor-transistor logic (TTL) technology or complementary metal oxide semiconductor (CMOS) logic technology. The operational speed of the nodes in turn constrains the throughput of the switching networks and hence limits the performance of the switching system as a whole. Improvements in the effective speed of operation of switching nodes can therefore improve the performance of the whole switching system. However, any contemplated improvements in the speed of operation of the node must heed other constraints, such as the above-described limitations on the number of contacts available on a circuit package.
In summary then, the prior art has achieved integration of a plurality of switching nodes into a single circuit package only with use of an undesirably large number of contacts to the circuit package. Furthermore, the art has been limited in switching network throughput by the switching speed of individual switching nodes.